The goals of this proposal are to help bring a better understanding of how viral packaging motors function and to find out the role of the components critical to their function. Using single virus and DNA manipulation techniques, we have the opportunity to extract an unprecedented amount of detailed information on how these systems operate. Furthermore, by exploring different viral packaging systems we can test whether certain classes of viruses all work using the same mechanisms. First, an experimental technique will be developed to investigate how lambda viruses package DNA. Second, the detailed mechanism in which the motor can take chemical energy and convert it to moving DNA will be investigated. Finally, the effect of critical proteins to the survival of this virus on its ability to package DNA will be explored. The fundamental information gathered from these experiments may aid the rational design of antiviral drugs. Specific Aims: 1. The universality of viral DNA packaging motors will be explored by developing a new optical tweezers assay for studying DNA packaging in bacteriophage A. Motor force, DNA translocation measurements, and their dependence on biochemical conditions will be extended to A. 2. The mechanochemistry of the lambda viral packaging motor will be elucidated by measuring ATP, ADP, and Pi dependence, pause distributions, and force measurements on packaging. 3. The specific roles of gpD and gpFI, proteins critical for lambda viral packaging, will be investigated. This research will be of interest to public health because the system that will be studied is expected to have similarities to relevant mammalian viruses such as herpesviruses, adenoviruses, and poxviruses. They are thought to share a common packaging mechanism, presumably powered by a similar molecular motor. By understanding the detailed mechanochemistry as well as the additional proteins necessary for the survival of these viruses, we may envision new strategies to regulate their infectivity.